1. Field of the Invention
The invention relates generally to methods and apparatuses for generating simulated smoke, and in particular to methods and apparatuses for generating simulated smoke that may be used for testing smoke and fire detection equipment.
2. Background Description
Aircraft smoke detection testing, for example, used to test the performance of smoke detection systems for cargo compartments of aircraft, has been a highly uncertain and often costly component of the airplane certification process. Whenever a cargo compartment or a smoke detection system is designed or changed significantly, aircraft manufacturers are required to demonstrate acceptable smoke detector performance. This typically involves generating smoke in an affected compartment during a test flight, and showing that the smoke detection system produces an alarm within the specified period of time.
In connection with ongoing efforts to increase aircraft safety, the U.S. Federal Aviation Administration (“FAA”) has recently elevated test requirements by demanding swifter detection of smaller smoke quantities. The present allowable smoke rate that must be detected is near the limit of many of the most current smoke detection systems, and therefore small variations in the generation rate of smoke during testing, due to factors such as ambient temperature variations, can dramatically increase the likelihood of inconsistent test results. Thus, it has become a challenge to provide not only a quantity of smoke that meets test criteria for certification of smoke detection systems, but also a repeatable and consistent quantity of smoke for tests of aircraft smoke detection equipment.
Existing smoke generator systems produce thermal aerosols for testing aircraft cargo hold smoke detection systems. Examples of such smoke generator systems include, for example, the Aviator, manufactured by Corona Integrated Technologies, Inc. and the ZZ101, manufactured by Siemens SAS. Both of these smoke generators produce mineral oil thermal aerosols. However, recent lab tests have shown that the oil temperature in the reservoirs of these generators greatly affects smoke production. Tests of the Siemens ZZ101 showed that oil cold-soaked at 35° F. produced approximately 40% of the smoke produced by oil warm-soaked at 105° F. Oil viscosity likely caused this behavior, as it changes significantly in the range of temperatures tested (the oil freezes at 14° F.). Tests of the Aviator smoke generator system produced similar results.
This variability of output with temperature adds much risk to aircraft certification efforts, as a smoke detection system that passes ground detection tests on a warm day can fail a flight test with a cooler or unheated cargo compartment. Alternately, a generator whose output registers a given smoke density during lab calibration will release less simulated smoke in the following days if those days happen to be cooler. Such sequences of events may result in costlier test efforts.
Accordingly, there is a need for smoke generation systems and methods that precisely control smoke generation rates and other relevant parameters, such as, for example smoke particle size (droplet size) and heat plume energy.
The present invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.